Equilibrium and Nonequilibrium Electrical Conductivity of a Potassium-Seeded Argon Plasma
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概要
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Experiments have been made on the electrical conductivity of argon-potassium and helium-potassium plasmas at atmospheric pressure. The gas, its container, and electrodes are heated uniformly in an electric furnace to a temperature ranging from 1300 to 1700℃. Thermal ionization of the potassium atoms makes the gas electrically conductive. Through the ionized gas an electric current of short duration is passed, the current density ranging from (10)^<-5> to 2 A/(cm)^2. As a function of the current density, the electric field in the plasma is determined with two electrostatic probes and effects of the sheath-voltages on the main electrodes are avoided. The gas temperature is not disturbed by the current because its duration is very short. With small current density the conductivity is independent of the current density and the plasma is in a thermal equilibrium. From the experimental value of conductivity the average cross section of a potassium atom for electron-momentum transfer is estimated to be 2.3×(10)^<-14>(cm)^2. For intermediate current density the conductivity becomes lower than the equilibrium value. The electrons may not be in Maxwellian distribution. The decrease in the conductivity is interpreted on the bases of the non-Maxwellian distribution of the electron energy and the decrease in the mobility of electrons at high electron temperature. The apparent conductivity at high current density is large, but the current density in the plasma may not be uniform.
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